Looking at the schematic here http://ax84.com/media/ax84_m276.gif what kind of output section is it. I think it is PP but no phase inverter.
THanks
THanks
Firefly question
- Thread starter SamBooka
- Start date
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It is push-pull. I have one as a bag of parts in the basement and hope to actually build it someday. Reviews and youtube videos are pretty strong.
I've built an amp based on the firefly output stage. It's called a self-split push pull. It uses a cheaper push pull output transformer and gives you more of the harmonics associated with a p-p amp. It's a fun little amp, loud for just practice at home, but even maxed out will struggle with a drummer. What would you expect from 1 watt. IMHO the self split doesn't give you much more power then single ended, but given the tubes used you got 2 valves so use them
Mine with a custom preamp
Mine with a custom preamp
Jebrone Lames
Banned
If you build one, add a bias switch to use a range of output tubes: 12AU7, 12BH7, ECC99.
The ECC99 will be 3 watts output.
The ECC99 will be 3 watts output.
Jebrone, do you have the details for the switched bias? Sounds like a worthwhile mod.
andyfromdenver
Friend of Leo's
Hi Jebrone, and OP, I for some reason couldn't find the firefly scheme on ax84 a while back when looking so thanks!
I recall some thread there that this super low watt PP output section is what's in the Marshall 1 watts. Is that correct?
I might be interested to do a mini 2204 circuit if so, though I like the switchable channel of this firefly.
I was gonna do a Marshall front end to single ended, but maybe this is the way to go to get the benefits of PP.
The self-split (no phase inverter) push pull circuit is pretty cool. It's similar to a long tail pair phase inverter. The signal enters the upper tube's grid and it acts as a normal, inverting gain stage but it also acts as a cathode follower since the two cathodes are tied together. The audio signal is passed to the lower tube's cathode and the lower tube's grid is held constant at ground so the cathode voltage fluctuations create a non-inverted amplified signal on its plate.
jipp
Friend of Leo's
looks like a fun bedroom amp.
chris.
chris.
jipp
Friend of Leo's
I've built an amp based on the firefly output stage. It's called a self-split push pull. It uses a cheaper push pull output transformer and gives you more of the harmonics associated with a p-p amp. It's a fun little amp, loud for just practice at home, but even maxed out will struggle with a drummer. What would you expect from 1 watt. IMHO the self split doesn't give you much more power then single ended, but given the tubes used you got 2 valves so use them
Mine with a custom preamp
View attachment 253705
looks like a bunch of fun to me.
chris.
Jebrone Lames
Banned
Rob, do a search on the AX84 site and it should come up. I used a DPDT switch and a 220R for the ECC99 and a 440R for the 12AU7 ,but please reconfirm those values while you do a search. The one drawback of the firefly is that it's a triode output. I ended up tearing mine down and building a self-split EL84 version of the Maggie 109.
The firefly's designer Doug h. (AX84) tore his down and built this: (link removed)
(link removed)
Thanks Jebrone.
I forgot one very cool thing you can do with the Firefly. Build the Firezog line out which turns the whole amp into a preamp or effects box ( if you use a bypass box) feeding any larger amp. Now you can play with the band and you have a touch responsive power amp distortion which can also feed into delay, reverb etc. Lots of fun.
andyfromdenver
Friend of Leo's
That's really cool. Kind of bridges the gap for tube amp designing into guitar pedal designing.
Marshall used a cathodyne and a LTP for their 1W amps. Originally I was going to do a Bassman build with 6AK6's but then I built my 5E3 amp. Ordered another PT so might do one yet. Was going to make it in a small metal enclosure so it could act as amp or preamp.
andyfromdenver
Friend of Leo's
That sounds killer! Thanks.
I haven't searched if those schemes were floating around the internet, thanks! Maybe I'll use one of the mini chassis I bought and do a low watt PP build.
I see a whole little industry of small amps as fx, I'm sure someone has tried, but maybe it wouldn't take off, I dunno.
Yea, I've used it as a "bedroom" amp and home (Still plenty loud to annoy the wife!) and then plug into a larger SS amp at practice, so I don't have to lug around a heavy tube amp.
KCStratMan
Tele-Afflicted
There is a big compartment of this forum that deals with stompboxes and pedals of all kinds with lots of discussion, arguments and opinions - I've ventured there a few times, kinda scary lots of mention of Rats and Screamers, but real tube overdrive pedals / preamps seem less well understood, mistrusted, and eschewed as too expensive in general. Some love evidenced for older BK Butler tube drivers, Duncan Twin Tube etc. I would like to invite design ideas from here amongst real live amp builders for a stand -alone preamp / recording amp. Full operating voltage, no "starved plates". Must have "all tube" signal path, no ss devices to induce clipping, etc. Looking for 2 switchable "channels" clean / dirty; or mild dirt / heavy distortion; or 3 channel clean/crunch/distortion. Looking for good 3 band EQ, maybe one "voicing option" switch, but not Super-Dumble complex controls and options. Looking for performance similar to Kingsley Juggler, Effectrode Blackbird, etc. Head box okay, pedal format not necessary. What can we design and build that would yield Fender cleans, Marshall crunch, and Soldano lead distortion? I will leave this thought here and start a new thread.
I like that Firezog mod for the Firefly.
KC that sounds great, I'll see you in the new thread.
KC that sounds great, I'll see you in the new thread.
KC, Many pedal builders want to stay away from the high voltage and transformers to do tubes. I did too, until I started working on tube amps. I'd say another factor is that what your looking for is even much more complex than most diy tube amps. Have you checked out AX84.com, the guys there would be able to build such a beast.
Oops, just saw the other thread. Check out AX84
Oops, just saw the other thread. Check out AX84
